Method of hydrolyzing polyacrylamide

ABSTRACT

Polyacrylamide dispersed in a polymeric latex may be hydrolyzed by the use of an alkali stable organic surfactant followed by the reaction of the polyacrylamide with an alkali metal hydroxide or quaternary ammonium hydroxide.

This is a continuation of copending Ser. No. 912,652 filed June 5, 1978,which in turn is a continuation-in-part of copending Ser. No. 840,446filed Oct. 7, 1977, now abandoned, which in turn is a continuation ofcopending Ser. No. 705,652 filed July 15, 1976, now abandoned, which inturn is a continuation-in-part of copending Ser. No. 514,961 filed Oct.15, 1974, now U.S. Pat. No. 3,998,777.

INTRODUCTION

This invention concerns a method of hydrolyzing polyacrylamide toprovide a polymer which has been found to be useful in thickening andflocculation applications. In particular, aqueous solutions of thehydrolyzed polyacrylamide of this invention have been found to provideexcellent results in the thickening and dewatering of industrial wastes,sewage wastes, and clarifications of turbid aqueous solutions. Inaddition the hydrolyzed polyacrylamide is used in secondary and tertiaryoil recovery processes to helf increase the amount of crude oilrecovered from underground oil-bearing formations. The use of thepolymer in this oil recovery process is becoming quite widespread inview of the current need to meet our crude oil requirements.

Typically these polymers are available as powders or as finely dividedsolids, which are dissolved in water to form aqueous solutions for usein the desired application. Great difficulty has been experienced indissolving the dry polymers, particularly hydrolyzed polyacrylamide dueto its slow dissolution time and because the dry polymer is not readilydispersable in water. The dry polymer has a tendency to form lumps whenplaced in contact with water. These lumps often taken quite a longperiod of time to dissolve, sometimes as long as 6-10 hours.

U.S. Pat. No. 3,624,019, Anderson et al, discloses a polymeric latexcomprising a water-in-oil emulsion which contains dispersed thereinfinely divided particles of a water-soluble vinyl addition polymer. Apreferred polymer disclosed therein is polyacrylamide. The emulsionscontaining polymer described therein are stable and when inverted in thepresence of water, the polymer goes into solution in a very short periodof time as compared to the dissolution of a dry solid polymer. Awater-in-oil polymerization process and method for making latex polymersis disclosed in Vanderhoff et al, U.S. Pat. No. 3,284,393.

It would be desirable to provide a hydrolyzed polyacrylamide polymer inthe form of the polymeric latex described above. However, up to thistime it has not been possible to hydrolyze a polymeric latex ofpolyacrylamide. During the hydrolysis reaction the polymeric latexbecomes unstable and the polymer present in the polymeric latexcoagulates and precipitates out of the water-in-oil emulsion therebyproducing a commercially useless product.

This invention provides a method of hydrolyzing polyacrylamide which ispresent in the form of a polymeric latex by the addition of an organicstabilizer or alkali stable organic surfactant to the polymeric latexprior to the hydrolysis. By the addition of the organic stabilizer, itis therefore possible to perform the hydrolysis to provide a polymericlatex of hydrolyzed polyacrylamide which is stable.

OBJECTS

It is therefore an object of this invention to provide a method ofhydrolyzing polyacrylamide.

It is also an object of this invention to provide a method ofhydrolyzing polyacrylamide, which is in the form of a polymeric latex.

Another object of this invention is to provide a stable polymeric latexof hydrolyzed polyacrylamide by the addition of an alkali stable organicsurfactant prior to the hydrolysis.

A further object is to provide an alkali stable organic surfactant foruse in hydrolyzing polyacrylamide.

A still further object is to provide a stable polymeric latex ofhydrolyzed polyacrylamide for use in secondary and tertiary oilrecovery, clarification of turbid aqueous solutions and for thickeningand dewatering of industrial and sewage wastes.

Other objects will appear hereinafter.

THE INVENTION

This invention provides a method of hydrolyzing polyacrylamidecomprising the steps of:

(A) Forming a polymeric latex comprising a water-in-oil emulsion whichcontains dispersed therein finely divided polyacrylamide;

(B) Adding to the polymeric latex an alkali stable organic surfactantcapable of forming a water-in-oil emulsion; and

(C) Reacting the polymeric latex containing the organic stabilizer withan alkali metal hydroxide or quaternary ammonium hydroxide to form ahydrolyzed polyacrylamide.

THE POLYMERIC LATEX

A polymeric latex is formed which comprises a water-in-oil emulsioncontaining dispersed therein finely divided polyacrylamide. Thesepolymeric lattices and their method of production are described in U.S.Pat. Nos. 3,284,393 and 3,624,019. These Patents are incorporated hereinby reference.

The molecular weight of the polyacrylamide may vary over a wide range,i.e., 10,000-25,000,000. The invention, however, finds its greatestusefulness when the molecular weight of the polyacrylamide is in excessof 1 million.

The oils used in preparing the polymeric latex may be selected from alarge group of organic liquids which include liquid hydrocarbons andsubstituted liquid hydrocarbons. A preferred group of organic liquidsare the hydrocarbon liquids which include both aromatic and aliphaticcompounds such as benzene, xylene, toluene, mineral oils, kerosenes, andnaphthas. A particularly useful oil from the standpoint of its physicaland chemical properties is the branch-chain isoparaffinic solvent soldby Humble Oil and Refining Company under the trade name ISOPAR M.Typical specifications of this narrow-cut isoparaffinic solvent are setforth below in Table I.

                  TABLE I                                                         ______________________________________                                                       Min-                                                           Specification Properties                                                                     imum    Maximum   Test Method                                  ______________________________________                                        Gravity, API at 60/60° F.                                                             48.0    51.0      ASTM D 287                                   Color, Saybolt 30                ASTM D 156                                   Aniline Point, °F.                                                                    185               ASTM D 611                                   Sulfur, ppm            10        ASTM D 1266.sup.1                            Distillation, ° F.        ASTM D 86                                    IBP            400     410                                                    Dry Point              495                                                    Flash Point, °F., (Pensky-                                                            160               ASTM D 93                                    Martens closed cup).                                                          ______________________________________                                         .sup.1 Nephelometric mod.                                                

The amounts of the components in the polymeric latex may vary over awide range. However, generally the polymeric latex is composed of 20-50%by weight of water, 10-40% by weight of oil and 20-40% by weight ofpolyacrylamide. It is generally necessary to employ an oil solubleemulsifying agent in order to maintain a stable emulsion. The amount ofemulsifying agent needed to provide an emulsion will have to bedetermined by routine experimentation. As a general rule it may be saidthat the amount of oil-soluble emulsifier may range from 0.1 to 30% byweight based on the weight of oil. To produce stable emulsions theamount of emulsifier will normally be within the range of 3-15% byweight of the oil. The preferred emulsifiers are the so-called low HLBmaterials which are well documented in the literature and are summarizedin the Atlas HLB Surfactant Selector. Although these emulsifiers areuseful in producing good water-in-oil emulsions, other surfactants maybe used as long as they are capable of producing these emulsions. Forinstance, certain high HLB surfactants are capable of producing stablewater-in-oil emulsions. A typical low HLB emulsifier is sorbitanmonooleate. Other emulsifiers are discussed in U.S. Pat. No. 3,284,393.

The emulsions may be prepared by any one of a number of methods. Oneparticular method is that taught in U.S. Pat. No. 3,284,393. Inaddition, the emulsions may be prepared by using high-speed agitation orultrasonic techniques.

THE ALKALI STABLE ORGANIC SURFACTANT

The organic surfactants used in this invention must be alkali stable andcapable of forming a water-in-oil emulsion. Any compound meeting theserequirements may be used, however due to variations in the polymericlatex, and hydrolysis agents, each organic stabilizer should be triedfirst on a small sample and be used on a case by case basis.

The organic stabilizer typically used is formed by the reaction of analiphatic hydrocarbon alcohol having from 10-20 carbon atoms with from2-10 moles of ethylene oxide per mole of the alcohol. Preferably thealcohol will have from 12-18 carbon atoms and will be reacted with 2-4moles of ethylene oxide per mole of the alcohol.

A preferred organic surfactant is formed by the reaction of one mole ofoleyl alcohol with two moles of ethylene oxide to form polyoxyethylene(2) oleyl alcohol. Another preferred organic stabilizer is formed by thereaction of one mole of lauryl alcohol with four moles of ethylene oxideto form polyoxyethylene (4) lauryl ether. These compounds are well knownand their preparations are commonly known to those skilled in the art.

In the preferred embodiment of this invention, the organic surfactant isadded to the polymeric latex and thoroughly mixed in a concentration offrom 0.10 to 15.0% by weight based on the polymeric latex. The preferredconcentration is from 0.5 to 3.0% by weight.

Another embodiment of this invention involves the forming of thepolymeric latex which comprises a water-in-oil emulsion which containsdispersed therein finely divided polyacrylamide and the organicstabilizer formed by the reaction of an aliphatic hydrocarbon alcoholhaving from 10-20 carbon atoms with from 2-10 moles of ethylene oxideper mole of the alcohol. This polymeric latex is then reacted with ahydrolysis agent to form a hydrolyzed polyacrylamide. The advantage ofthis embodiment of the invention is that there is one less step in themethod. The organic stabilizer being already present in the polymericlatex.

THE HYDROLYSIS

The polymeric latex containing the organic stabilizer is reacted with ahydrolysis agent. The hydrolysis agents may be alkali metal hydroxidesor quaternary ammonium hydroxides. Typically, alkali metal hydroxidesinclude lithium, sodium and potassium hydroxides. A typical quaternaryammonium hydroxide is tetra methyl ammonium hydroxide.

In the practice of the invention the hydrolysis agent used should beadded to the polymeric latex as an aqueous solution slowly and withmixing. The preferred hydrolysis agents used in the invention are alkalimetal hydroxides and more specifically sodium, potassium, and lithiumhydroxides with the most preferred being about a 50% aqueous solution ofthe alkali metal hydroxide. The concentration of the solution of thealkali metal hydroxide is within the range of 0.2-30% by weight based onthe polymeric latex and preferably 4-12% by weight based on thepolymeric latex. However, the percentage of hydrolysis agent used willalways vary to the degrees of hydrolysis desired with higher percentageof the hydrolysis agent being used for higher degrees of hydrolysis.

While solutions of about 50% concentration of the Alkali metalhydroxides are convenient to use, it is important to note that higher orlower concentrations of alkali metal hydroxides in aqueous media may beused. Conditions favoring lower concentration of the hydrolysis agentinclude the desire for low levels of hydrolysis and stability factors.Conditions favoring higher concentrations include the desire for a highdegree of hydrolysis without excessive dilution, and for stabilityreasons.

The hydrolysis may be conducted at room temperature but more favorableresults are obtained at elevated temperatures. Generally the reactionmaybe performed within the range of from 10°-70° C. The preferredtemperature range is from 35°-55° C. The length of time for hydrolysisdepends upon the reactants, their concentration, reaction conditions andthe degree of hydrolysis desired. It has been experimentally determinedthat polyacrylamide may be hydrolyzed according to the procedure setforth herein to a degree of between 5-80%. Depending upon the reactionconditions described above, typically a 20-60% hydrolysis is obtained,with the preferred range being 30-50%. This hydrolysis procedure and allof the reaction conditions and ranges described herein apply to bothembodiments of this invention: that is, (1) the formation of thepolymeric latex with the alkali stable organic surfactant and (2) theaddition of the alkali stable organic surfactant to a polymeric latex.With the use of the organic surfactant, it is possible to hydrolyze thepolymeric latex of polyacrylamide.

The hydrolyzed polyacrylamide is dispersed throughout the water-in-oilemulsion, similar to those emulsions disclosed in Anderson et al, U.S.Pat. No. 3,624,019. This polymer latex may be inverted in a similarmanner to that disclosed in Anderson et al. The polymer latex releasesthe hydrolyzed polyacrylamide in water in a very short period of time.Generally, a surfactant is added to either the polymer-containingemulsion or to the water into which it is to be dissolved. The placementof a surfactant into the water causes the emulsion to rapidly invert andrelease the polymer in the form of an aqueous solution. The surfactantslisted in Anderson et al have been found to easily invert the hydrolyzedpolyacrylamide, however, due to variations in the polymeric laticessurfactants used for inversion should be tried on a case by case basis.The invention can be more readily understood by the following examples.

EXAMPLE 1

A polyacrylamide latex was prepared for hydrolysis studies.

A two liter three-neck reaction vessel was charged with 340 g. of anisoparaffinic solvent previously described as ISOPAR M, and having anaverage molecular weight of 175-180, and 20 g. of sorbitan monooleate asan emulsifier. To this was added 40 g. of acrylamide, 180 g. of water,0.4 ml. of 2% EDTA (ethylene diamine tetraacetic acid) and a drop of 50%sodium hydroxide. Over a 30 minute period of time, the temperature wasraised to 30° C. and then to 45° C. within 10 minutes as 10 mls. of 8%vazo catalyst is added. Vazo catalyst is a well-known catalyst and is2,2'azobis (isobutronitrile). The amount of catalyst is 0.2% by weightbased on the monomer. After 30 minutes, 200 mls. of a monomer solutionis added. The monomer solution contains the following:

Acrylamide: 360 g.

Water: 250 g.

Boric Acid: 7.2 g.

EDTA: 3.6 ml.

50% sodium hydroxide: 0.5 g.

The temperature is kept between 43°-48° C. for 11/2 hours. Then, 200mls. of the monomer solution is again added. The temperature is keptbetween 44°-50° C. for 11/2 hours, after which a third addition of 200mls. of the monomer solution is added. After about two hours, thereaction is stopped and a good latex recovered without particles.

The molecular weight was over 5,000,000 and the intrinsic viscosity wasover 10.0.

EXAMPLE 2

One hundred fifty grams of the latex of Example 1 was charged to a 500ml. reaction flask. To this was added 2.52 g. of polyoxyethylene (2)oleyl ether and stirred about 400 r.p.m. at room temperature for 25minutes. Then, at 26° C., 16.95 g. of 50% sodium hydroxide was addedover a five minute period. The temperature increased to 32.5° C. Thereaction mixture was stirred at about 400 r.p.m. After one hour, sampleNumber 1 was taken. An hour later sample Number 2 was taken. Eighteenhours later, sample Number 3 was removed.

The samples were worked-up in the following way: A sample of the latexas diluted with 100 ml. of ISOPAR M solvent having an average molecularweight of 175 to 180. This was then added to 1 liter of a mixed solventcontaining 50% each by volume of acetone and methanol, filtered anddried 16 hours under vacuum at 40° C.

The following table II shows the amount of latex in each samples, driedweight, the percent acrylate and amide in the product as measured byinfra-red analysis and the viscosity at a concentration of 1.0% indeionized water.

                  TABLE II                                                        ______________________________________                                        Sample Grams     Dried    %      %      Viscosity                             No.    Latex     Weight   Acrylate                                                                             Amide  (cps)                                 ______________________________________                                        1      22.68 g.  7.93 g.  16     84     10,000                                2      21.80     7.80     26     74     26,000                                3      23.40     8.80     40     60     25,500                                ______________________________________                                    

This example shows the effect of time on the hydrolysis.

EXAMPLE 3

This example was run the same as Example 2 except a higher temperaturewas used, namely 45° to 50° C.

Samples were taken at one hour, two hours, and after about 20 hours. Thefollowing Table III shows the results of the respective samples. Thesame work-up was used as in Example 2.

                  TABLE III                                                       ______________________________________                                        Sample Weight    Dried    %      %      Viscosity                             No.    Latex     Weight   Acrylate                                                                             Amide  (cps)                                 ______________________________________                                        1      26.42 g.  10.2 g.  36     64     26,500                                2      24.50 g.  9.71 g.  37     63     16,500                                3      24.60     9.70 g.  39     61     28,000                                ______________________________________                                    

EXAMPLE 4

This example uses a different alkali stable organic surfactant. A 500ml. three necked-distillation flask is equipped with a stirrer,thermometer, sampling tube, reflux condenser, and a hot water bath. Onehundred fifty grams of the latex of Example 1 is charged to the reactionflask. Then, 2.53 g. of polyoxyethylene (4) lauryl ether is added to thelatex at 42°-45° C. After stirring for about ten minutes at 400 r.p.m.,17.15 g. of 50% sodium hydroxide is added dropwise. A moderate viscosityincrease is noted. The reaction is held at 42°-45° C. for one hour. Amolderate darkening is observed. Sample 1 is removed. After anotherhour, sample 2 is removed. The same work-up is used as in Example 2.

                  TABLE IV                                                        ______________________________________                                        Sample Weight    Dried    %      %      Viscosity                             No.    Latex     Weight   Acrylate                                                                             Amide  (cps)                                 ______________________________________                                        1      21.6      8.9      40     60     26,000                                2      21.5      8.0      40     60     26,000                                ______________________________________                                    

EXAMPLE 5

Another latex was prepared using a greater amount of emulsifier andalkali stable organic surfactant. A latex was prepared in the same wayas Example 1 except that instead of 20 g. of sorbitan monooleate, 60 g.(15% by weight) of polyoxyethylene (2) oleyl ether was used.

EXAMPLE 6

After the polymerization of Example 5 was completed, 50 g. of the latexwas placed in a reaction vessel. Then, 3.36 g. (20% by weight) of thesodium salt of alkyl acryl polyether sulfonate was added as anemulsifier. This emulsifier is sold under tradename of Triton X-200.Thus, the total amount of emulsifier and stabilizer is 35% by weightbased on the polymer. Then, 2.72 g. of 50% sodium hydroxide (10 molepercentage based on polyacrylamide) was added and hydrolysis proceededas in Example 2. The polymer as measured by titration showed 12%acrylate.

EXAMPLE 7

This example was run in the same way as Example 6 except the amount of50% sodium hydroxide was 0.91 g. (5 mole percentage based onpolyacrylamide). The result was that the polymer as measured bytitration showed 6% acrylate.

As is readily apparent to anyone skilled in the art, the examplesdemonstrate a useful method for the hydrolysis of polyacrylamide, andproduce a stable product readily inverted into aqueous solution.

What is claimed is:
 1. The method of hydrolyzing polyacrylamide whichcomprises the steps of:A. forming a polymeric latex comprising awater-in-oil emulsion which contains dispersed therein finely dividedpolyacrylamide and an organic surfactant which is alkali stable and willform a stable water-in-oil emulsion said polymeric latex comprising from20 to 50% by weight of water, from 10 to 40% by weight of oil, and from20 to 40% by weight polyacrylamide, and from 0.10 to 15% by weight ofthe alkali stable organic surfactant; and then, B. reacting saidpolymeric latex containing the organic stabilizer with an alkali metalhydroxide or quaternary ammonium hydroxide whereby a stable water-in-oilemulsion of finely divided hydrolyzed polyacrylamide is formed.
 2. Themethod of claim 1 wherein said alkali stable organic surfactant rangesfrom 0.5 to 3.0% by weight based on the polymeric latex.
 3. The methodof claim 1 wherein said alkali stable organic surfactant ispolyoxyethylene (2) oleyl ether formed by the reaction of one mole ofoleyl alcohol with two moles of ethylene oxide.
 4. The method of claim 1wherein said alkali stable organic surfactant is polyoxyethylene (4)lauryl ether formed by the reaction of one mole of lauryl alcohol withfour moles of ethylene oxide.
 5. The method of claim 1 wherein saidalkali metal hydroxide is an aqueous solution of sodium hydroxide ofabout 50 weight percent.
 6. The method of claim 1 wherein said alkalimetal hydroxides are from the group consisting of sodium hydroxide,potassium hydroxide and lithium hydroxide.
 7. The method of claim 1wherein said alkali metal hydroxide is an aqueous solution of about 50%concentration by weight and said solution ranges from 0.2 to 30% byweight based on the polymeric latex.
 8. The method of claim 1 whereinsaid alkali metal hydroxide is in aqueous solution of about 50%concentration by weight and said solution ranges from 4 to 12% by weightbased on the polymeric latex.
 9. The method of claim 1 wherein saidpolyacrylamide is hydrolyzed to from 5 to 80% by weight.
 10. The methodof claim 1 wherein said polyacrylamide is hydrolyzed to from 20 to 60%by weight.
 11. The method of claim 1 wherein said polyacrylamide ishydrolyzed to from 30 to 50% by weight.